Magnetic separation of positive and negative ignitor firing pulses



14, 1955 A. H. MITTAG EI'AL 2,759,125

MAGNETIC SEPARATION OF POSITIVE AND NEGATIVE IGNITOR FIRING PULSES FiledApril 25, 1955 ZERO J i g Invent, or's: Albert H. Mittag Burnice D.Bedfor'd,

Their Attorneyhired MAGNETIC SEPARATIGN 9F POSITIVE AND NEGATIVE IGNITQRFRING PULSES Albert E. Editing, Schenectady, and Bur-nice D. Redford,Scotia, N. Y., assignors to General Electric Company, a corporation ofNew York Application April 25,1955, Serial No. 503,696

Ciaims. Cl. 315-252 tional current conducting devices are not employedto block inverse voltages.

In order to obtain the desired precision of operation of the electricdischarge devices of the type contemplated herein, a supply circuit isusually provided which impresses voltages of predetermined wave form,such as voltages of peaked Wave form, on the ignitors or startingelectrodes thereof. Only a small inverse voltage is permissible on theignitors or starting electrodes of such discharge devices or they willeither be destroyed or the life thereof will be materially reduced. As aconsequence, it is common practice to couple the ignitors of thedischarge devices to the supply circuit by means of a transformer,connecting each ignitor in series with a unidirectional currentconducting device and connecting the series combination across thetransformer output circuit. The unidirectional, current conductingdevices are poled to pass current in a direction to initiate dischargeof the device and block or eliminate reverse current halfcycles of thealternating current supply. The unidirectional current conductingdevices are generally rectifiers or" the selenium type which are subjectto failure. Failure of the rectifiers allows the application of inversevoltage on the ignitors and consequently results in the destruction or asubstantial reduction in the life thereof.

Accordingly, it is an object of this invention to provide an improvedenergizing circuit for starting electrodes of pool cathode type valueswherein the application of reverse voltages on the starting electrodesis substantially eliminated without the use of blocking rectifiers.

Briefly stated, in accordance with the invention, the usual blockingrectifiers are eliminated by placing a saturable impedance device havinga biasing winding in series circuit relationship with each ignitorelectrode and supplying a biasing voltage to the biasing windings whichsaturates the reactor and opposes the magnetizing effect of a reversecurrent in the circuit. That is to say, each saturable reactor issaturated by the direct current ampere turns of the biasing windingsthereon in the same sense as the positive ignitor current tends tosaturate them and, in a sense, opposite to that in which a reverseignitor current tends to saturate them. In this way, each saturablereactor, being already saturated with ampere turns of a sense to aid themagnetizing effect of positive ignitor current, presents a very highimpedance to negative ignitor current since its flow is opposed by thesaturated impedance device. Thus, the inverse voltage on the ignitors ismaintained at a permissible value without the use of blockingrectifiers.

The novel features which are believed to be charatceristic of thisinvention are set forth with particularity in the appended claims. Theinvention itself, however, both as to its organization and method ofoperation, together Patent 0 2,759,125 Fatented Aug. 14, 1956 withfurther objects and advantages thereof, will be better understood fromthe following description taken in connection with the accompanyingdrawing in which:

Fig. 1 is a schematic representation of a pair of mercury pool cathodedischarge devices and their energizing circuits in which the inventionis embodied; and

Fig. 2 is a diagram illustrating an operating characteristic of thecircuit of Fig. 1.

Referring now to Fig. l, the invention is illustrated in a system forsupplying a direct current load circuit having a positive conductor 10and a negative conductor 11 from an alternating current supply 12. Thetranslating or rectifying apparatus of the illustrated circuit utilizesan anode supply transformer 13 having its primary winding 14 connectedacross the alternating current supply 12 and its center tapped secondarywinding 15 connected to supply the plate potential for the two vaporelectric discharge devices or valves 16 and 17.

Each of the two vapor electric discharge devices is of theimmersion-ignitor or cathode pool type and each has an anode 18, a pooltype cathode 19, and an ignitor or starting electrode 20 immresed in thecathode pool. As previously indicated, the secondary 15 of the anodesupply transformer 13 is connected between the anodes 18 of the twovalves 16 and 17. The center point or center tap of the transformersecondary Winding 15 is connected to the negative conductor 11 or" theload circuit and the two cathodes 19 of the valves 16 and 17 areconnected to the positive conductor 10. The excitation circuits forsupplying potential to the ignitors 20 and cathodes 19 as hereinafterdescribed are designed to provide the proper control to these elementsso that the valves act as rectifiers. It will be understood, however,that the valves could be arranged to act as an inverter and that theinvention is applicable to the type valves contemplated herein whenoperated as either a rectifier or an inverter. Also, the invention isapplicable to the use of a single valve such as 16 or 17.

The potential on the ignitors 20 and cathodes H of the valves 16 and 17is supplied from the center tapped secondary or output winding 25 of anignitor supplying transformer 23 which has its primary or input winding24 connected to be energized from the main alternating current source 12through a phase shifting circuit 21 and a voltage peaking circuit 22.The center tap of the ignitor supplying transformer secondary winding 25is connected to the cathode 19 of each of the tubes, and thus it is alsoconnected to the positive conductor 19 of the direct current loadcircuit. The individual ignitors 24) of the valves 16 and 17 areconnected in series with main windings 26 and 27 respectively, ofsaturable core impedance devices 28 and 29, and each such series circuitis connected across one-half the secondary winding 25 of the anodesupplying transformer. As illustrated, the ignitors 20 are connected tobe energized from opposite end terminals of the secondary Winding, andthus they are supplied with a positive firing potential on alternatehalf cycles of the alternating current supply.

The saturable core impedance devices 23 and 29 are employed in serieswith the ignitors 24 to reduce inverse voltages on the ignitors, i. e.,to suppress negative ignitor current. in order to accomplish thisresult, the saturable core impedance devices 28 and 29 are provided withdirect current biasing windings 3i and 31 respectively. The biasingwindings as illustrated are connected in series with each other andacross a direct current source 32 which preferably is of sutficientmagnitude to provide enough ampere turns to saturate each reactor. Thebiasing windings are connected in their direct current circuit in such amanner that their magnetizing action on their respective reactors is toaid the magnetizing efiect of a positive firing half cycle flowing inthe main winding and oppose the magnetizing effect of a negative ignitorcurrent. Reactors 28 and 29 then offer very little impedance to apositive firing current in their respective circuits since they arealready saturated in an aiding direction but present a very highimpedance to negative ignitor currents which tends to build up ampereturns in opposition to the established direct current ampere turns. Theactual ignitor voltage wave form is illustrated in Fig. 2 of the drawingand will be explained in more detail hereinafter.

The wave peaking circuit 22 is employed to provide an alternatingcurrent of peaked wave form to be applied to the ignitors 20. Asillustrated, the peaking circuit is of the type disclosed and claimed inU. S. Patent 2,431,- 903, granted December 2, 1947, on an application ofE. F. W. Alexanderson and A. H. Mittag. The wave peaking circuit 22comprises a saturable firing reactor 33 and a firing capacitance 34,which together constitute a resonant circuit of the non-linear type.That is, the circuit is non-linearly resonant with respect to themagnitude of the voltage of source 12, the inductive reactance of firingreactor 33 having a value which is substantially greater than thecapacitive reactance of the phase shift circuit 21 (described in detailhereinafter) within the lower region of the source voltage, and smallerthan the capacitive reactance thereof within the upper region so that animpulse of voltage is produced when the firing reactor 33 saturates.These impulses occur twice during each cycle of voltage at timesrelative to the supplied voltage wave which are determined by thesaturation of the non-linear firing reactor 33. A linear reactor 35 isconnected between the phase shift circuit 21 and peaking circuit 22 toprevent discharge of the capacitor 34 back to the phase shift circuitand to limit the magnitude of the current derived from the supply.

in order to shift the. phase of the firing voltage impressed on theignitors 2t) and thereby control the magnitude of the unidirectionalload voltage, the previously referred to phase shifting circuit 21 isinterposed between the alternating current source 12 and the peakingcircuit 22. The phase shifting circuit illustrated is of the typedisclosed and claimed in U. S. Patent 2,3 62,294, granted November 7,1944, to Albert H. Mittag. The phase shift circuit utilized comprisesthe series combination of an inductive reactance 36 and a capacitor 37,and a saturable core impedance device 38 having its main winding 39connected in one supply line. The output of the phase shift circuit istaken across the series combination of the inductive reactance 3.6 andcapacitor 37.

The saturable core impedance device 38 is provided with a suitablecontrol means such as a control winding 48'. The control winding 49 isconnected to be supplied from a direct current source 41 and may becontrolled manually by means of a current controlling variableresistance 42 or in response to a predetermined controlling influencesuch as the voltage of an associated circuit. The variable inductiveimpedance 38 cooperates with the impedance of the circuit into which itworks, i. e., its load circuit, to constitute a phase shifting network.The phase of the output voltage of the network may be shifted over awide range. by varying the impedance of the reactance 38. In thismanner, the time of firing of valves 16 and 17 is determined and,consequently, the. magnitude of the direct current potential to the loadcircuit is determined within limits. The series circuit comprising theinductance. 36. and capactor 37 in the phase, shift circuit is providedto maintain the voltage supplied by the circuit to its load at asubstantially constant value throughout .an appreciable range. of phaseshift of the output voltage.

Utilizing the circuits illustrated, the voltage impressed upon theprimary winding 24 of. the ignitor supplying transformer 23' is of apeaked wave form having symmetrical positive and negative half cyclesoccurring every electrical degrees. The duration of the peaks areapproximately eighteen electrical degrees. Since the reactors 28 and 29in the ignitor circuits are arranged to suppress inverse voltage peaksin their respective circuits, the voltage wave form on the ignitor 20 ineither circuit comprises positive peaks of approximately eighteenelectrical degrees duration and spaced by 342 electrical degrees, i. e.,occurring once every 360 electrical degrees.

This wave form is illustrated in Fig. 2.

Also, as may be seen from Fig. 2, a small inverse voltage, representedby the magnitude 0, flows for the remaining 342 electrical degrees ofeach cycle. This small inverse voltage is not enough to damage theignitors 20. For the best results, the applied voltage peak should be ofas short duration as possible since the areas of the positive andnegative portions of the wave tend to become equal to each other.Therefore, the shorter the positive pulse, the smaller the inversevoltage 0 applied to the ignitor 20'.

In practice, it would be possible to peak the voltage from the secondaryof the supply transformer 25 rather than peaking the voltage suppliedthereto. This arrangement would, however, require careful selection ofcircuit elements and would require elements of corresponding highratings.

Connecting the main windings 26 and 27 of the saturable reactors in theoutput circuit of the ignitor supplying transformer secondary 25, asillustrated, has definite advantages over connecting such windings inthe primary circuit. It would appear that the magnetizing ampere turnsrequired of reactor biasing windings and reactor winding insulation,problems would be minimized if the saturable reactor were placed in theprimary circuit of the circuit of the ignitor supplying transformer.However, the main winding of a reactor, which is connected in serieswith the primary winding of a transformer, must necessarily carry thetransformer no load current (i. e., the magnetizing current and thecurrent required to supply hysteresis a'nd eddy current losses). Thus,the biasing winding must furnish enough ampere turns to overcome theefiect of the transformer no load current in the main winding if it isto maintain the reactor in its saturated condition. When the saturablereactor is connected in the secondary circuit, the biasing windings arenot required to supply ampere turns to overcome such a current.

Additional factors are the tendency of the, areas of the positive andnegative portions of the applied voltage wave to become equal to eachother in the transformer primary and secondary circuits and the factthat the impedance of the ignitors is non-linear. That is to say thatthe impedance of the ignitors is higher with respect to negativecurrents than with respect to positive currents flowing therein and,consequently, are instrumental in reducing reverse current flow. Sincethe ignitors themselves tend to limit the flow of current in a reversedirection in their circuits, the ampere turns which must be suppliedby abiasing winding of a saturable reactor in such a circuit to maintain thesaturable impedance device in its saturated condition can be reducedaccordingly. Therefore, since the biasing windings of a saturable coreimpedance device in the output circuit of the ignitorsupplyingtransformer does not have to overcome the transformer no load current,and since the reverse' current in the secondary circuit is normallyreduced due; to the non-linearity of the ignitor impedance, a much lowerbias suffices for areactor in the secondary circuit" than is requiredfor a reactor placed in the primary circuit to suppress inverse voltagesin the ignitors.

From the foregoing analysis and description, it will be apparent that,by the use of the saturable impedance devices 2 8 and 29in the ignitorcircuits, the need for blocking rectifiers therein is eliminated. Itwillalso be apparent that by the combined treatment of the saturable'impedance device and the peaking circuit 22, the possibility of aharmful inverse voltage occurring on the ignitors 20 is further reduced.

While the invention has been shown and described as being applied to aparticular system of connections and embodying various devicesdiagrammatically shown, it will be obvious to those skilled in the artthat changes and modifications may be made without departing from theinvention. Consequently, the aim is to cover such changes andmodifications as fall within the true spirit and scope of our inventionas defined by the appended claims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In combination, an electric discharge device of the cathode pool typehaving a starting electrode, a transformer having a primary inputWinding to be energized with alternating current and a secondary outputwinding, and a saturable reactance device having a main winding and abiasing Winding, the main winding of said saturable reactance device andsaid starting electrode and the cathode of said discharge device beingconnected in series with each other across at least a part of the outputWinding of said transformer, the biasing winding of said saturablereactance device being energized with direct current, the magntizingeflect of said biasing winding being to saturate said saturablereactance device, the magnetizing eflect of said main winding being toaid and oppose the magnetizing action of said biasing winding onalternate half-cycles of said alternating current so that said saturableimpedance device tends to pass and suppress current flow on alternatehalf cycles.

2. A circuit for energizing the starting electrode of a cathode pooltype electric discharge device comprising a transformer having a primaryinput Winding to be energized with alternating current and a secondaryoutput winding, and a saturable impedance device having a main Windingand a biasing winding, said main winding of said saturable impedancedevice and at least a part of said secondary output winding of saidtransformer being connected in series with each other and interconnectedwith the starting electrode, said biasing winding of said saturableimpedance device being energized with direct current, the magnetizingefiect of said biasing winding being in opposition to the magnetizingefiect of alternate half cycles of said alternating current.

3. In combination, a pair of electric discharge devices of the cathodepool type having a starting electrode, said discharge device beingconnected to conduct alternate half cycles of alternating current, atransformer having a primary winding connected to be energized from asource of alternating current energy and a secondary output winding, anda pair of saturable reactance devices, each of said saturable reactancedevices having a main winding and a biasing winding, the main win-dingof each saturable reactance device being connected in series with one ofsaid starting electrodes and its associated cathode, each of said seriescircuits being connected across at least a portion of said secondaryoutput winding, said biasing winding on each of said saturable impedancedevices being connected across a source of direct current energy, saidbiasing windings being arranged in such a manner that their magnetizingaction aids and opposes the magnetizing action of the current in theassociated main winding on alternate half cycles so that each saturableimpedance device tends to pass and suppress current How on alternatehalf cycles.

4. In combination, a voltage peaking circuit for producing analternating voltage which is symmetrical with respect to positive andnegative half cycles and which is of peaked wave form, an electricdischarge device of the cathode pool type having a starting electrode, atransformer having a primary input winding connected to said peakingcircuit for energization thereby and a secondary output winding, and asaturable reactance device having a main Winding and a biasing winding,the main winding of said saturable reactance device and said startingelectrode and the cathode of said discharge device being connected inseries with each other across at least a part of the output winding ofsaid transformer, the biasing winding of said saturable reactance devicebeing energized with direct current, the magnetizing ellect of saidbiasing winding being sufiicient to saturate said saturable reactancedevice, the magnetizing efliect of said main winding being to aid andoppose the magnetizing effect of said biasing winding on alternate halfcycles of said alternating current so that said saturable impedancedevice tends to pass and suppress current flow on alternate half cycles.

5. In combination, a voltage peaking circuit for producing analternating voltage which is symmetrical with respect to positive andnegative half cycles and which is of a peaked wave form, a pair ofelectric discharge devices of the cathode pool type having a startingelectrode, said discharge devices being connected to conduct alternatehalf cycles of alternating current, a transformer having a primary inputwinding connected to said peaking circuit for energization thereby and asecondary output winding, and a pair of saturable reactance devices,each of said saturable reactance devices having a main Winding and abiasing winding, the main winding of each saturable reactance devicebeing connected in series with one of said starting electrodes and itsasscciated cathode, each of said series circuits being connected acrossat least a portion of said secondary output winding, said biasingwinding on each of said saturable impedance devices being connectedacross a source of direct current energy, said biasing windings beingarranged in such a manner that the magnetizing efiect aids and opposesthe magnetizing effect of the current in the associated main winding onalternate half cycles so that each saturable impedance device tends topass and suppress current flow on alternate half cycles.

No references cited.

